We propose to test the hypothesis that changes in lung and regional chest wall mechanical properties (i.e., impedances) are correlated with postoperative complications. Our studies will include three stages, each will answer important questions about respiratory mechanics in health and disease and provide background information to test our overall hypothesis. We will employ methods that we have recently developed that enable accurate measurement of regional chest wall impedance in the normal range of breathing amplitude and frequency. In those experiments where the airway is intubated, we will additionally measure lung impedance. In the first stage, we will examine how regional impedances of the chest wall in healthy subjects change throughout the course of daily activity, as the respiratory muscles are called upon to perform in many non-respiratory tasks (lifting, trunk turning, changing posture, different forms of exercise, etc.) We will be able to decide how certain posture, different forms of exercises affect chest wall impedance and how regional properties interact to determine the properties of the chest wall as a whole. In the second interact to determine the properties of the chest wall as a whole. In the second stage, we will study the effects of anesthesia and muscle paralysis on lung and regional chest wall impedances in healthy subjects in the laboratory. In particular, we will evaluate the extent of regional differences in chest wall impedance: if large, the differences may cause unequal distribution of ventilation and thereby lead to impairment of gas exchange, a major postoperative problem. In the third stage, we will make measurements of lung and regional chest wall impedances in patients before and after various types of surgery. The measurements before surgery will allow us to accumulate a data base of accurate, standardized measurements from a diverse sampling of patients, with healthy and diseased respiratory systems. These data will strengthen our ability to understand and diagnose respiratory disorders. The measurements after surgery, in the recovery room, will enable us to test for correlations between respiratory impedances and postoperative complications such as atelectasis. We will try to develop objective criteria for onset and reversal of respiratory postoperative complications, assist diagnosis and determine the efficacy of treatment regimens.